A Cu-1.5 wt.%Ti/Diamond(55 vol.%)composite was fabricated by hot forging from powder mixture of copper,titanium and diamond powders at 1050?C.A nano-thick TiC interfacial layer was formed between the diamond particle ...A Cu-1.5 wt.%Ti/Diamond(55 vol.%)composite was fabricated by hot forging from powder mixture of copper,titanium and diamond powders at 1050?C.A nano-thick TiC interfacial layer was formed between the diamond particle and copper matrix during forging,and it has an orientation relationship of(111)TiC//(002)Cu&[110]TiC//[110]Cuwith the copper matrix.HRTEM analysis suggests that TiC is semicoherently bond with copper matrix,which helps reduce phonon scattering at the TiC/Cu interface and facilitates the heat transfer,further leading to the hot-forged copper/diamond composite(referred as to Cu-Ti/Dia-0)has a thermal conductivity of 410 W/m K,and this is about 74%of theoretical thermal conductivity of hot-forged copper/composite(552 W/m K).However,the formation of thin amorphous carbon layer in diamond particle(next to the interfacial TiC layer)and deformed structure in the copper matrix have adverse effect on the thermal conductivity of Cu-Ti/Dia-0 composite.800℃-annealing eliminates the discrepancy in TiC interface morphology between the diamond-{100}and-{111}facets of Cu-Ti/Dia-0 composite,but causes TiC particles coarsening and agglomerating for the Cu-Ti/Dia-2 composite and interfacial layer cracking and spallation for the Cu-Ti/Dia-1 composite.In addition,a large amount of graphite was formed by titanium-induced diamond graphitization in the Cu-Ti/Dia-2 composite.All these factors deteriorate the heat transfer behavior for the annealed Cu-Ti/Dia composites.Appropriate heat treatment needs to be continually investigated to improve the thermal conductivity of hot-forged CuTi/Dia composite by eliminating deformed structure in the copper matrix with limit/without impacts on the formed TiC interfacial layer.展开更多
Thermomechanical processing(TMP)is especially crucial for metastableβtitanium alloys,which has received significant attention in the community for a long time.In this contribution,the processing-responding behaviour ...Thermomechanical processing(TMP)is especially crucial for metastableβtitanium alloys,which has received significant attention in the community for a long time.In this contribution,the processing-responding behaviour including microstructure evolution process,texture variation mechanism,and un-derlying deformation process of powder metallurgy Ti-5553 alloy in a wide processing parameter range was comprehensively investigated.Thermal physical simulation was performed on the alloy at temper-atures ranging from 800℃ to 1100℃,and strain rates between 0.001 s^(−1) and 10 s^(−1),to varied defor-mation degrees of 20%-80%height reduction.It was found that the processing parameters(i.e.temper-ature,strain rate,and deformation degree)are influential on the deformation process and resultant mi-crostructure.Varied microstructural evolution processes forβphase including flow localization,dynamic recovery,dynamic recrystallization,and grain coarsening are activated in different processing domains,while different evolution mechanisms forαphase including dynamic precipitation,phase separation,dy-namic coarsening,and mechanical shearing also play their roles under different processing conditions.In particular,four exceptional evolution mechanisms ofαprecipitation which have not been previously reported in titanium alloys were discovered and clearly demonstrated,more specifically,they are multi-interior twinning,internal compositing,layered coarsening and selective diffusion-actuated separation.After the establishment of comprehensive microstructural evolution mechanism maps,the guidance for precise processing and the knowledge reserve extension for deformation process of metastableβtita-nium alloys can be effectively achieved.展开更多
Nano-lamellar Ti_(3)Al/TiAl(α2/γ)alloy with significantly improved nanohardness was prepared using dual-wire-fed electron beam-directed energy deposition(EB-DED)in this study.This investigation focused on the evolut...Nano-lamellar Ti_(3)Al/TiAl(α2/γ)alloy with significantly improved nanohardness was prepared using dual-wire-fed electron beam-directed energy deposition(EB-DED)in this study.This investigation focused on the evolution of the colony shape and lamellar thickness of the Ti-43Al lamellar alloy at different heights.Nanoindentation tests were employed to evaluate deformation resistance,and numerical simulations provided deeper insights into the deposition process.The results indicate that the colonies are mostly columnar,except for a few equiaxed colonies at the top.Rapid cooling significantly refines theα2 lamellae,resulting in an average spacing of 218 nm and thickness of 41 nm.Additionally,substantial microstrain and a nonequilibrium Al distribution lead to a significant generation ofγvariants,refining theγlamellae to 57 nm.Abundantγ/γ’andα2/γinterfaces,along with fineα2 phases,contribute to improved deformation resistance.Consequently,the nano-lamellar TiAl alloy exhibited a notable 32%increase in nanohardness(8.3 GPa)while maintaining a similar modulus(197 GPa)to conventionally prepared alloys.This study holds significant promise for advancing high-performance TiAl alloys through the dual-wire-fed EB-DED process.展开更多
Mg_(x)(Ni_(0.8)La_(0.2))_(100-x),where x=60,70,80,exhibiting a nanocrystalline microstructure,were prepared through the crystallization of amorphous alloys.The investigation encompassed the phase constitution,grain si...Mg_(x)(Ni_(0.8)La_(0.2))_(100-x),where x=60,70,80,exhibiting a nanocrystalline microstructure,were prepared through the crystallization of amorphous alloys.The investigation encompassed the phase constitution,grain size,microstructural stability,and hydrogen storage properties.Crystallization kinetics,along with in-situ high-energy XRD characterization,revealed a concentrated and synchronous crystallization of Mg_(2)Ni and RE-Mg-Ni ternary phases with the increase in La and Ni content.The attributed synchronous crystallization process was found to be a result of the close local affinity of Mg_(2)Ni and RE-Mg-Ni ternary phases,as assessed by the thermodynamic Miedema model.Significant secondary phase pinning effect,arising from the high likelihood of well-matching phase structures between Mg_(2)Ni,LaMg_(2)Ni,and LaMgNi_(4),was validated through both the edge-to-edge matching model prediction and experimental observation.Thefine and homogeneous microstructure was shown to be a consequence of fast crystallization kinetics and the secondary phase pinning effect.Improved activation performance and cycling stability were observed,stemming from grain refinement and excellent microstructural stability.Our study provides insights into mechanism of grain refinement of nanocrystalline microstructure tailored by phase constitution and crystallization kinetics in the amorphous-crystallization route.We also demonstrate the potential of material design guided by phase equilibria and crystallographic predictions to improve nanocrystalline with excellent microstructural stability.展开更多
To enhance the Young’s modulus(E)and strength of titanium alloys,we designed titanium matrix composites with intercon-nected microstructure based on the Hashin-Shtrikman theory.According to the results,the in-situ re...To enhance the Young’s modulus(E)and strength of titanium alloys,we designed titanium matrix composites with intercon-nected microstructure based on the Hashin-Shtrikman theory.According to the results,the in-situ reaction yielded an interconnected microstructure composed of Ti_(2)C particles when the Ti_(2)C content reached 50vol%.With widths of 10 and 230 nm,the intraparticle Ti lamellae in the prepared composite exhibited a bimodal size distribution due to precipitation and the unreacted Ti phase within the grown Ti_(2)C particles.The composites with interconnected microstructure attained superior properties,including E of 174.3 GPa and ultimate flexural strength of 1014 GPa.Compared with that of pure Ti,the E of the composite was increased by 55% due to the high Ti_(2)C content and interconnected microstructure.The outstanding strength resulted from the strong interfacial bonding,load-bearing capacity of interconnected Ti_(2)C particles,and bimodal intraparticle Ti lamellae,which minimized the average crack driving force.Interrupted flexural tests revealed preferential crack initiation along the{001}cleavage plane and grain boundary of Ti_(2)C in the region with the highest tensile stress.In addition,the propagation can be efficiently inhibited by interparticle Ti grains,which prevented the brittle fracture of the composites.展开更多
Discontinuously reinforced titanium matrix composites(DRTMCs)with a network structure have been extensively researched due to their superior combination of strength and ductility.However,their fatigue performance has ...Discontinuously reinforced titanium matrix composites(DRTMCs)with a network structure have been extensively researched due to their superior combination of strength and ductility.However,their fatigue performance has remained unknown.In order to elucidate the fatigue behavior of DRTMCs,a tension-tension fatigue test was performed on a TiB/nearα-Ti composite with network structure.The results showed that the variability of fatigue lifetime increased as the stress level decreased.Fractography analysis indicated that fatigue crack initiation was associated with facet formation,while the subsequent propagation was hindered by the network structure comprising TiB whiskers and silicides.Crystallographic characterization further revealed that facets formed due to a combination of shear and normal stress.The reduction in fatigue lifetime was attributed to an increase in the effective slip length,which was influenced by the orientation of grains near the crack-initiation sites toward basal slip in the life-limiting specimen.Quasi in situ observation suggested that the crack initiation was facilitated by both basal and prismatic slip ofα-Ti as well as fracture of TiBw.Crack propagation was found to be associated with basal and prismatic slip systems with high Schmid factors,regardless of whether the crack was intergranular or intragranular.展开更多
In order to improve the microstructure and mechanical properties,the hot compressive deformation with 50%height reduction at 1100℃was conducted on a Ti_(2)C-Ti cermet.The results showed that the lamellar Ti precipita...In order to improve the microstructure and mechanical properties,the hot compressive deformation with 50%height reduction at 1100℃was conducted on a Ti_(2)C-Ti cermet.The results showed that the lamellar Ti precipitates in Ti_(2)C grains were transformed to bimodal size distribution,which was approximately 290 nm and 5.8μm in diameter,respectively,after the hot deformation.The bimodal Ti precipitates suppressed{011}cleavage surfaces of Ti_(2)C during flexural fracture,which resulted in an 18.5%increment of strength.This phenomenon can be attributed to the bimodal Ti precipitates that decreased the average crack driving force due to their gentle variation in elastic modulus compared with the monolithic lamellar Ti precipitates.The present work can guide further deformation and mechanical property improvement of Ti_(2)C cermets.展开更多
The hot deformation behavior and microstructure evolution of GH3536-TiB2composites fabricated by powder metallurgy(PM)were examined in the temperature range of 950–1150℃ and strain rate range of 0.001–1 s^(-1). The...The hot deformation behavior and microstructure evolution of GH3536-TiB2composites fabricated by powder metallurgy(PM)were examined in the temperature range of 950–1150℃ and strain rate range of 0.001–1 s^(-1). The hot compression stress-strain curves and the constitutive equation were obtained. In addition, the hot processing map was drawn, which indicated that the appropriate hot working window was 950–1050℃/0.001–0.1 s^(-1)and 1050–1100℃/0.001–0.01 s^(-1). The microstructure analysis showed that the splitting and spheroidization of M3B2led to a decrease in size and volume fraction at 950–1100℃. At 1150℃,the eutectic microstructure of M_(3)B_(2)+ γ was formed due to the dissolution of M_(3)B_(2), which caused macroscopic cracking of the deformed sample. Additionally, the deformation temperature and the strain rate had little effect on the size and volume fraction of M_(3)B_(2). Besides, discontinuous dynamic recrystallization(DDRX) and continuous dynamic recrystallization(CDRX) were found in the deformed microstructure, while the former was dominant. Within the test range of this work, the dynamic recrystallization(DRX) fraction of the deformed composites was high due to the bulging nucleation of numerous interfaces. The DRX grain size increased with increasing deformation temperature or decreasing strain rate. Texture analysis showed that the deformation texture of <101>//compression direction RD existed in the matrix when the deformation temperature was below 1100℃, and the texture type became <001>//RD at 1100℃. Additionally, it was also found that the <001>//RD texture was formed in M3B2under the strain rates of 0.1 and 0.01 s^(-1).展开更多
基金supported by the Air Force Office of Scientific Research under award number FA2386-17-14025。
文摘A Cu-1.5 wt.%Ti/Diamond(55 vol.%)composite was fabricated by hot forging from powder mixture of copper,titanium and diamond powders at 1050?C.A nano-thick TiC interfacial layer was formed between the diamond particle and copper matrix during forging,and it has an orientation relationship of(111)TiC//(002)Cu&[110]TiC//[110]Cuwith the copper matrix.HRTEM analysis suggests that TiC is semicoherently bond with copper matrix,which helps reduce phonon scattering at the TiC/Cu interface and facilitates the heat transfer,further leading to the hot-forged copper/diamond composite(referred as to Cu-Ti/Dia-0)has a thermal conductivity of 410 W/m K,and this is about 74%of theoretical thermal conductivity of hot-forged copper/composite(552 W/m K).However,the formation of thin amorphous carbon layer in diamond particle(next to the interfacial TiC layer)and deformed structure in the copper matrix have adverse effect on the thermal conductivity of Cu-Ti/Dia-0 composite.800℃-annealing eliminates the discrepancy in TiC interface morphology between the diamond-{100}and-{111}facets of Cu-Ti/Dia-0 composite,but causes TiC particles coarsening and agglomerating for the Cu-Ti/Dia-2 composite and interfacial layer cracking and spallation for the Cu-Ti/Dia-1 composite.In addition,a large amount of graphite was formed by titanium-induced diamond graphitization in the Cu-Ti/Dia-2 composite.All these factors deteriorate the heat transfer behavior for the annealed Cu-Ti/Dia composites.Appropriate heat treatment needs to be continually investigated to improve the thermal conductivity of hot-forged CuTi/Dia composite by eliminating deformed structure in the copper matrix with limit/without impacts on the formed TiC interfacial layer.
基金support from National Natural Science Foundation of China(No.52101122).Q.Zhao,R.Torrens,F.Yang and L.Bolzoni would like to gratefully acknowledge the support from New Zealand Ministry of Business,Innovation and Employment(No.UOWX1402)supported by Science and Technology Major Project of Shaanxi Province(No.2020-zdzx04-01-02)+1 种基金Key Research Plan of Shaanxi Province(No.2021KW-18)Young Talents Promotion Project of China Association for Science and Technology(No.YESS20200335).
文摘Thermomechanical processing(TMP)is especially crucial for metastableβtitanium alloys,which has received significant attention in the community for a long time.In this contribution,the processing-responding behaviour including microstructure evolution process,texture variation mechanism,and un-derlying deformation process of powder metallurgy Ti-5553 alloy in a wide processing parameter range was comprehensively investigated.Thermal physical simulation was performed on the alloy at temper-atures ranging from 800℃ to 1100℃,and strain rates between 0.001 s^(−1) and 10 s^(−1),to varied defor-mation degrees of 20%-80%height reduction.It was found that the processing parameters(i.e.temper-ature,strain rate,and deformation degree)are influential on the deformation process and resultant mi-crostructure.Varied microstructural evolution processes forβphase including flow localization,dynamic recovery,dynamic recrystallization,and grain coarsening are activated in different processing domains,while different evolution mechanisms forαphase including dynamic precipitation,phase separation,dy-namic coarsening,and mechanical shearing also play their roles under different processing conditions.In particular,four exceptional evolution mechanisms ofαprecipitation which have not been previously reported in titanium alloys were discovered and clearly demonstrated,more specifically,they are multi-interior twinning,internal compositing,layered coarsening and selective diffusion-actuated separation.After the establishment of comprehensive microstructural evolution mechanism maps,the guidance for precise processing and the knowledge reserve extension for deformation process of metastableβtita-nium alloys can be effectively achieved.
基金supported by the National Key Research and Development Program of China(No.2022YFF0609000)the National Natural Science Foundation of China(Nos.51871075,52171034 and 52101037).
文摘Nano-lamellar Ti_(3)Al/TiAl(α2/γ)alloy with significantly improved nanohardness was prepared using dual-wire-fed electron beam-directed energy deposition(EB-DED)in this study.This investigation focused on the evolution of the colony shape and lamellar thickness of the Ti-43Al lamellar alloy at different heights.Nanoindentation tests were employed to evaluate deformation resistance,and numerical simulations provided deeper insights into the deposition process.The results indicate that the colonies are mostly columnar,except for a few equiaxed colonies at the top.Rapid cooling significantly refines theα2 lamellae,resulting in an average spacing of 218 nm and thickness of 41 nm.Additionally,substantial microstrain and a nonequilibrium Al distribution lead to a significant generation ofγvariants,refining theγlamellae to 57 nm.Abundantγ/γ’andα2/γinterfaces,along with fineα2 phases,contribute to improved deformation resistance.Consequently,the nano-lamellar TiAl alloy exhibited a notable 32%increase in nanohardness(8.3 GPa)while maintaining a similar modulus(197 GPa)to conventionally prepared alloys.This study holds significant promise for advancing high-performance TiAl alloys through the dual-wire-fed EB-DED process.
基金supported by National Natural Science Foundation of China(51761034,51961032,51962028 and 52261041)Innovation Foundation of Inner Mongolia University of Science and Technology(2019YQL03)+2 种基金Major Science and Technology Project of Inner Mongolia(2021ZD0029)Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region(NJYT23005,NJYT23007)Program for Innovative Research Team in Universities of Inner Mongolia Autonomous Region(NMGIRT2401).
文摘Mg_(x)(Ni_(0.8)La_(0.2))_(100-x),where x=60,70,80,exhibiting a nanocrystalline microstructure,were prepared through the crystallization of amorphous alloys.The investigation encompassed the phase constitution,grain size,microstructural stability,and hydrogen storage properties.Crystallization kinetics,along with in-situ high-energy XRD characterization,revealed a concentrated and synchronous crystallization of Mg_(2)Ni and RE-Mg-Ni ternary phases with the increase in La and Ni content.The attributed synchronous crystallization process was found to be a result of the close local affinity of Mg_(2)Ni and RE-Mg-Ni ternary phases,as assessed by the thermodynamic Miedema model.Significant secondary phase pinning effect,arising from the high likelihood of well-matching phase structures between Mg_(2)Ni,LaMg_(2)Ni,and LaMgNi_(4),was validated through both the edge-to-edge matching model prediction and experimental observation.Thefine and homogeneous microstructure was shown to be a consequence of fast crystallization kinetics and the secondary phase pinning effect.Improved activation performance and cycling stability were observed,stemming from grain refinement and excellent microstructural stability.Our study provides insights into mechanism of grain refinement of nanocrystalline microstructure tailored by phase constitution and crystallization kinetics in the amorphous-crystallization route.We also demonstrate the potential of material design guided by phase equilibria and crystallographic predictions to improve nanocrystalline with excellent microstructural stability.
基金financially supported by the National Key R&D Program of China(No.2021YFB3701203)the National Natural Science Foundation of China(Nos.U22A20113,52201116,52071116,and 52261135543)+1 种基金Heilongjiang Touyan Team ProgramChina Postdoctoral Science Foundation(No.2022M710939).
文摘To enhance the Young’s modulus(E)and strength of titanium alloys,we designed titanium matrix composites with intercon-nected microstructure based on the Hashin-Shtrikman theory.According to the results,the in-situ reaction yielded an interconnected microstructure composed of Ti_(2)C particles when the Ti_(2)C content reached 50vol%.With widths of 10 and 230 nm,the intraparticle Ti lamellae in the prepared composite exhibited a bimodal size distribution due to precipitation and the unreacted Ti phase within the grown Ti_(2)C particles.The composites with interconnected microstructure attained superior properties,including E of 174.3 GPa and ultimate flexural strength of 1014 GPa.Compared with that of pure Ti,the E of the composite was increased by 55% due to the high Ti_(2)C content and interconnected microstructure.The outstanding strength resulted from the strong interfacial bonding,load-bearing capacity of interconnected Ti_(2)C particles,and bimodal intraparticle Ti lamellae,which minimized the average crack driving force.Interrupted flexural tests revealed preferential crack initiation along the{001}cleavage plane and grain boundary of Ti_(2)C in the region with the highest tensile stress.In addition,the propagation can be efficiently inhibited by interparticle Ti grains,which prevented the brittle fracture of the composites.
基金financially supported by the National Key R&D Program of China(No.2021YFB3701203)the National Natural Science Foundation of China(NSFC,Grant Nos.52171137,52261135543 and U22A20113)the Heilongjiang Provincial Natural Science Foundation of China(Grant No.TD2020E001).
文摘Discontinuously reinforced titanium matrix composites(DRTMCs)with a network structure have been extensively researched due to their superior combination of strength and ductility.However,their fatigue performance has remained unknown.In order to elucidate the fatigue behavior of DRTMCs,a tension-tension fatigue test was performed on a TiB/nearα-Ti composite with network structure.The results showed that the variability of fatigue lifetime increased as the stress level decreased.Fractography analysis indicated that fatigue crack initiation was associated with facet formation,while the subsequent propagation was hindered by the network structure comprising TiB whiskers and silicides.Crystallographic characterization further revealed that facets formed due to a combination of shear and normal stress.The reduction in fatigue lifetime was attributed to an increase in the effective slip length,which was influenced by the orientation of grains near the crack-initiation sites toward basal slip in the life-limiting specimen.Quasi in situ observation suggested that the crack initiation was facilitated by both basal and prismatic slip ofα-Ti as well as fracture of TiBw.Crack propagation was found to be associated with basal and prismatic slip systems with high Schmid factors,regardless of whether the crack was intergranular or intragranular.
基金supported by the National Key R&D Program of China(Grant No.2021YFB3701203)the National Natural Science Foundation of China(Grant Nos.52171137,52071116,52192593)+2 种基金the Heilongjiang Provincial Natural Science Foundation of China(Grant No.TD2020E001)the Heilongjiang Touyan Team ProgramChina Postdoctoral Science Foundation(Grant No.2022M710939)。
文摘In order to improve the microstructure and mechanical properties,the hot compressive deformation with 50%height reduction at 1100℃was conducted on a Ti_(2)C-Ti cermet.The results showed that the lamellar Ti precipitates in Ti_(2)C grains were transformed to bimodal size distribution,which was approximately 290 nm and 5.8μm in diameter,respectively,after the hot deformation.The bimodal Ti precipitates suppressed{011}cleavage surfaces of Ti_(2)C during flexural fracture,which resulted in an 18.5%increment of strength.This phenomenon can be attributed to the bimodal Ti precipitates that decreased the average crack driving force due to their gentle variation in elastic modulus compared with the monolithic lamellar Ti precipitates.The present work can guide further deformation and mechanical property improvement of Ti_(2)C cermets.
基金supported by the National Key R&D Program of China (Grant No. 2021YFB3701203)the National Natural Science Foundation of China (Grant Nos. U22A20113, 52171137, 52201156 and 52071116)+2 种基金Heilongjiang Touyan Team Program, Heilongjiang Provincial Natural Science Foundation of China (Grant No. TD2020E001)Heilongjiang Postdoctoral Fund (Grant No. LBH-Z20058)Key Laboratories Foundation (Grant No. 6142910220206)。
文摘The hot deformation behavior and microstructure evolution of GH3536-TiB2composites fabricated by powder metallurgy(PM)were examined in the temperature range of 950–1150℃ and strain rate range of 0.001–1 s^(-1). The hot compression stress-strain curves and the constitutive equation were obtained. In addition, the hot processing map was drawn, which indicated that the appropriate hot working window was 950–1050℃/0.001–0.1 s^(-1)and 1050–1100℃/0.001–0.01 s^(-1). The microstructure analysis showed that the splitting and spheroidization of M3B2led to a decrease in size and volume fraction at 950–1100℃. At 1150℃,the eutectic microstructure of M_(3)B_(2)+ γ was formed due to the dissolution of M_(3)B_(2), which caused macroscopic cracking of the deformed sample. Additionally, the deformation temperature and the strain rate had little effect on the size and volume fraction of M_(3)B_(2). Besides, discontinuous dynamic recrystallization(DDRX) and continuous dynamic recrystallization(CDRX) were found in the deformed microstructure, while the former was dominant. Within the test range of this work, the dynamic recrystallization(DRX) fraction of the deformed composites was high due to the bulging nucleation of numerous interfaces. The DRX grain size increased with increasing deformation temperature or decreasing strain rate. Texture analysis showed that the deformation texture of <101>//compression direction RD existed in the matrix when the deformation temperature was below 1100℃, and the texture type became <001>//RD at 1100℃. Additionally, it was also found that the <001>//RD texture was formed in M3B2under the strain rates of 0.1 and 0.01 s^(-1).
